Landorus-Therian

Pros:

-Nice 145 Atk
-Great defensive bulk with Intimidate
-Forces switch outs to attackers like MHera, MPinsir, etc.
-As mentioned, great vs Sand.
-VERY easy to switch in to other Pokemon.
-Plethora of sets
-Has little checks and counters. The only two I can think of is Greninja and Keldeo, even then Greninja usually dies with scarf sets.
-Checks so many physical sweepers
-Counters a decent amount of Pokemon.
-Only 2 weaknesses, with Ice being nonexistent.

Cons:

-No reliable recovery; and you really need to keep him alive.
-91 Spe isn't favorable.
-Sometimes Scarf does not really help you out.
-I can't think of more cons. This thing is SOO fucking good.

Landorus I:

Pros:

-Great ability; paired with LO, 2x SE moves with STAB should do 4.2x damage then normal.
-101 speed just breaks the 100 Spe barrier, with things like MGarde,Mew,Jirachi,Victini,Celebi, etc. exist.
-Amazing coverage. Psychic, Sludge bomb, Earth Power and Knock off.
-Stall does not like it.
-3 great sets
-Counters/Checks a plethora of Pokemon
-Sweeps better than your mom in bed with me

Cons:

-Defenses aren't too favorable. I see it usually die quicker than Lando T.
-Setup takes time, and as forementioned, it's defenses aren't helping it with that.
-If your a decent player, it's extremely predictable. Azumarill is out? Switch to a steel type you conveniently placed on your team.
-Should I run Knock off? Calm mind, Psychic, Sludge wave, Rock Polish, Earth Power... Quite the amount to fit on 4 moves!